1. Field of the Invention:
The present invention relates, in general, to friction clutches, and in particular, to centrifugal friction clutches in which the frictional elements engage at a predetermined speed of rotation imparted by the input power means.
2. Information Disclosure Statement:
Centrifugal friction clutches which engage at a predetermined rotational speed are useful in combination with motors or engines that have useful torque ranges only at high rotational speeds. Examples of such engines include well-known small displacement gasoline engines used in go-cart racing. One of the problems encountered with such a frictional clutch on such an engine having useful torque only at high RPM is the high relative rotational speed between the input and output of the clutch, necessitating high rates of slippage during the engagement of the clutch. A well-known solution for this problem, particularly when the motor drives an output shaft through a reduction gearing system, is to place the clutch after the reduction gearing system, i.e., directly on the output shaft rather than on the (higher RPM) motor, thereby reducing the slippage that must occur between the input and output portions of the clutch. However, such a solution places a premium on the weight of the clutch because the inertial load presented by the clutch to the motor is thereby increased through the reduction gears between the motor and the clutch.
Additionally, in some applications such as go-cart racing, artificial weight constraints are placed on the total weight of the vehicle in which the clutch is used, and any weight reduction of the clutch may be put to more productive uses elsewhere on the vehicle. Known attempts at creating a centrifugal friction clutch have been complex and heavy, employing a multiplicity of balls or weights to engage the clutch mechanism, and lack ease of adjustability of the rotational speed of engagement of the clutch. Such prior attempts employed transmission disks within the engagement mechanism which are known to warp and produce a very complex clutch mechanism which requires frequent maintenance.
It is therefore desirable to have a lightweight centrifugal friction clutch which can be quickly and readily assembled and disassembled, and which provides for easily adjusting the rotational speed at which the clutch engages.
A preliminary patentability search in Class 192, subclasses 105CE and 105CF produced the following patents, some of which may be relevant to the present invention: Dysterud, U.S. Pat. No. 699,461, issued May 6, 1902; Woodward, U.S. Pat. No. 1,203,833, issued Nov. 7, 1916; Fellows, U.S. Pat. No. 1,256,120, issued Feb. 12, 1918; Bryson, U.S. Pat. No. 1,771,525, issued Jul, 29, 1930; Tranaas, U.S. Pat. No. 2,011,427, issued Aug. 13, 1935; Zahradnik et al., U.S. Pat. No. 2,789,674, issued Apr. 23, 1957; and Gubelmann, U.S. Pat. No. 2,915,159, issued Dec. 1, 1959.
Additionally, Horstman, U.S. Pat. No. 4,111,291, issued Sep. 5, 1978, and Gebhart, U.S. Pat. No. 4,856,637, issued Aug. 15, 1989, describe centrifugal clutches as might be used with go-carts.
While each of the above patents disclose centrifugal clutches, none disclose or suggest the present invention. More specifically, none of the above patents disclose or suggest a centrifugal friction clutch for transmission of torque from a source means for supplying rotational power to an output means for receiving said rotational power, said clutch comprising: a clutch housing rotationally driven by said source means; a wheel mounted for rotation within said clutch housing and secured for simultaneous rotation with said output means; a clutch band encircling said wheel and secured from rotation relative to said clutch housing; and, centrifugal means for tightening said clutch band about said wheel for frictional contact therewith, thereby causing said wheel to rotate with said clutch housing.
Dysterud, U.S. Pat. No. 699,461, describes a centrifugal clutch in which a pair of weighted arms force a pair of clutch shoes into an outer V-shaped groove on a clutch wheel. Similarly, Gubelmann, U.S. Pat. No. 2,915,159, describes a centrifugal clutch in which a multiplicity of weighted arms force a multiplicity of clutch shoes outward into an inner V-shaped groove on a clutch member. Neither Dysterud nor Gubelmann has a clutch band like the present invention.
Woodward, U.S. Pat. No. 1,203,833, describes a centrifugal clutch in which a pair of adjustably weighted arms each tighten one of a corresponding pair of semicircular clutch bands about a clutch drum. Fellows, U.S. Pat. No. 1,256,120, describes a similar pair of weighted arms operating a pair of semicircular clutch bands. The present invention uses no such partially circular clutch bands, but instead employs a clutch band that encircles the clutch wheel.
Tranaas, U.S. Pat. No. 2,011,427, merely describes a non-centrifugal band clutch in which a primary clutch band causes engagement of a main clutch band.
Zahradnik et al., U.S. Pat. No. 2,789,674, describes an inertial-centrifugal clutch in which counterbalanced weights on either end of an arm cause a multi-turn helical wire to constrict about a clutch drum. The present invention has no such multi-turn helical wire about a clutch drum.
Bryson, U.S. Pat. No. 1,771,525, describes a plurality of centrifugal weights that gearably and rotatably engage a band clutch about a clutch wheel, adjustably biased by a spring.
Horstman, U.S. Pat. No. 4,111,291, describes a centrifugal clutch which uses pivoting weights to frictionally engage a set of concentric clutch plates and disks. The present invention has no such concentric clutch plates or disks.
Gebhart, U.S. Pat. No. 4,856,637, describes a centrifugal clutch which uses pivoting weights to bias a conical pressure plate against the face of a conical clutch drum. Unlike the present invention, the Gebhart patent has no clutch band.